1. Field of the Invention
The present invention relates to touch panels and, particularly, to a carbon nanotube based touch panel and a display device using the same.
2. Discussion of Related Art
Following the advancement in recent years of various electronic apparatuses, such as mobile phones, car navigation systems and the like, toward high performance and diversification, there has been continuous growth in the number of electronic apparatuses equipped with optically transparent touch panels at the front of their respective display devices (e.g., liquid crystal panels). A user of any such electronic apparatus operates it by pressing or touching the touch panel with a finger, a pen, a stylus, or another like tool while visually observing the display device through the touch panel. Therefore, a demand exists for touch panels that provide superior visibility and reliable operation.
Up to the present time, different types of touch panels, including resistance, capacitance, infrared, and surface sound-wave types, have been developed. The capacitance-type touch panel has advantages such as high accuracy and excellent transparency, and thus has been widely used.
A conventional capacitance-type touch panel includes a glass substrate, a transparent conductive layer, and four electrodes. The material of the transparent conductive layer is selected from a group consisting of indium tin oxide (ITO) and antimony tin oxide (ATO). The electrodes are made of metal and are separately formed on a surface of the transparent conductive layer. Further, a protective layer is formed on the surface of the transparent conductive layer that faces away from the substrate. The material of the protective layer has insulative and transparent characteristics.
In operation, an upper surface of the touch panel is pressed/touched with a touch tool, such as a user's finger or an electrical pen. Visual observation of a screen on the liquid crystal display device provided on a back side of the touch panel is allowed. In use, due to an electrical field of the user, a coupling capacitance forms between the user and the transparent conductive layer. For high frequency electrical current, the coupled capacitance is a conductor, and thus the touch tool takes away a little current from the touch point. Currents flowing through the four electrodes cooperatively replace the current lost at the touch point. The quantity of currents supplied by the four electrodes is directly proportional to the distances from the touch point to the electrodes. A touch panel controller is used to calculate the proportion of the four supplied currents, thereby detecting coordinates of the touch point on the touch panel.
With the advent of roll-to-roll technology, e-papers (i.e., microencapsulated electrophoretic displays), flexible liquid crystal displays, and flexible organic light emitting displays (OLEDs) have been developed. Accordingly, a touch panel used with such flexible displays should be flexible too. However, the glass substrate of the above-described conventional touch panel is rigid. As such, the conventional touch panel is unsuitable for use with a flexible display. In addition, the ITO layer of the conventional touch panel has generally poor mechanical durability, low chemical endurance, and uneven resistance over an entire area of the touch panel. Furthermore, the ITO layer has relatively low transparency in humid environments. All the above-mentioned problems of the ITO layer tend to yield a touch panel with relatively low sensitivity, accuracy, and brightness. Moreover, the ITO layer is generally formed by means of ion-beam sputtering, and this method is relatively complicated.
What is needed, therefore, is to provide a flexible touch panel and a display device using the same having good durability, and high sensitivity, accuracy, and brightness.